Every process flow application will contain some degree of pressure build-up or pressure loss within the liquid or gas stream as it progresses through each stage of the process. Process engineers understand the specific flow characteristics of their respective processes and how pressure can either have a positive effect on the end product result or can have an adverse effect that can create a safety concern for personnel, damage critical process equipment & components and potentially lead to costly product loss. Pressure relief valves are an integral safety component designed into process flow systems, storage devices, transportation and delivery systems to protect against overpressure and under pressure conditions that may occur.
The primary purpose of a pressure relief valve is protection of life, property and product by relieving an unwanted situation before a harmful action can occur within the process pipeline or process vessels. There are many systems employed today to control pressure, temperature and flow within the process by means of electronics, pneumatics, and hydraulics. The pressure relief valve is an integral part of these systems with one exception. A pressure relief valve must be able to function at all times, even during a power failure when system controls may be inoperable. This function is created by the process fluid itself and in essence is the power source for the pressure relief valve.
The design, selection, sizing and use of a pressure relief valve will be dependent upon the conditions and fluids or gases within the process system. Thus, pressure relief valves should be mechanically simple and consistently reliable in their performance, along with having the diversity to be applied to many different process flow applications. The only major design features that should be taken into consideration are materials of construction for external and internal components, pressure components rating; as well as, seat and seal material selections.
There are a number of terms associated with relief valves with the generic term Pressure Relief Valve (PRV) being the most recognized. Other terms are Safety Valve (SV), Pressure Safety Valve (PSV) and Relief Valve (RV). It should be noted that PRV’s and PSV’s are not the same. The difference being PSV’s have a manual lever which can be opened in case of emergencies. Pilot-Operated Safety Relief Valve (POSRV), Low Pressure Safety Valve (LPSV), Vacuum Pressure Safety Valve (VPSV), and Low and Vacuum Pressure Safety Valve (LVPSV) are also terms associated with these valves but have specific applications they are designed for.